The present invention relates generally to devices for extracorporeal treatment of physiological fluids of organism, in particular, a hemoperfusion device for blood detoxification.
Dialysis is a commonly used physical treatment that removes excess water, electrolytes, urea and toxins from a patients physiological fluid. It is known to perform dialysis by passing physiological fluids such as blood along one side of a dialysis membrane and a special dialysate liquid along the other side. The known dialysis membranes are generally permeable to small molecular weight components of solutions and these components, by diffusing through the membrane, are exchanged between the above two liquids. Toxic metabolites of the physiological fluid, after passing the membrane, can thus be removed from the organism by the flow of the dialysate liquid. However, diffusion is a relatively slow process, so that 3 to 4 hours are needed for a sufficient clearance of blood. Moreover, the removal of larger toxic components from blood, the so called xe2x80x9cmiddle molecular weight toxinsxe2x80x9d, is much too slow, if possible at all, by the technique, because even the modern high permeable membranes used for hemodialysis must have a cut-off below 40-50 kD. This technique is useless if large toxic compounds are needed to be removed from the physiological fluid, such as endotoxins or tissue destruction products. In some acute cases of poisoning or drug overdose, the hemodialysis technique can prove to be too slow, as the diffusion of toxins trough the membrane would require such a long time, that would make the whole treatment impractical. Another disadvantage of the hemodialysis treatment is that it requires a complicated and expensive equipment and highly skilled medical personal and, therefore, cannot be quickly provided in emergency situations outside an adequate medical institution.
A much faster technique for removing unwanted compounds from a physiological fluid is the adsorption. It is known to pass the blood through a cartridge with activated carbon or polymeric adsorbent. Such a hemoperfusion treatment can be very efficient for rapid removing of both small and middle molecular weight toxins from blood or plasma. With the recent development of adsorption technologies, extremely efficient selective and non-selective polymeric adsorbing materials become available. The drawback of this technique is that highly efficient adsorbing materials are generally not hemocompatible. They quickly cause a series of adverse reactions of biological systems, complement activation and, finally, clotting of blood.
In order to enhance the biocompatibility, the adsorbing materials have to be chemically modified. Usually, polar functional groups or hemocompatible polymeric chains are introduced onto the surface of polymer beads, as suggested for example in U.S. Pat. No. 5,773,384 by Davankov et al. (1998). Korshak et al. in U.S. Pat. No. 4,140,652, (1978) suggested binding and cross-linking human serum albumin on the surface of a polystyrene-type adsorbing material. All these coverings, however, dramatically reduce the rate of mass transfer, slow down the adsorption process, diminish the adsorption capacity of the material in a reasonable period of time available for the patient treatment. Needless to say that any additional chemical treatment of the base adsorbing material increases its prize.
The above high requirements to the hemocompatibility of the adsorbing materials can be reduced significantly if blood cells and especially platelets and white blood cells are prevented from contacting directly the surface of the adsorbent. In other words, after separating cellular material of blood by some kind of hemofiltration, the remaining plasma can be quickly detoxificated with an efficient and inexpensive sorbent material.
Several kinds of continuous hemofiltration have been suggested. Gorsuch and Atkin (U.S. Pat. No. 5,151,082, 1992) suggest hollow fiber hemofiltration membranes to be surgically introduced into patients veins, in order to take plasma, instead of the whole blood, forthe subsequent extracorporeal treatment.
Another procedure and device is also known, as disclosed for example in the article xe2x80x9cThe Concept of Sorbents in Hemodialysisxe2x80x9d, published in xe2x80x9cThe International Journal of Artificial Organsxe2x80x9d volume 21, no. 6, 1998, pages 303-308. In this procedure a device is proposed which includes a hemofilter, a bioseparator and a hemodialyzer. The hemofilter separates the blood, so as to retain the blood cells and allow passage of a liquid component of the blood. The liquid component of the blood is supplied to the bioseparator which accommodates charcoal or adsorbing resin and is purified there, and then the purified liquid component together with the cells are supplied into the hemodializer. A similar system consisting of three separate units, a hemofiltration cartridge, a plasmaperfusion unit, and a hemodialyser, was earlier described in U.S. Pat. No. 5,194,157 (1993) by Ghezzi et al.
A complicated system, that allows a simultaneous combination of dialysis and filtration procedures, is subject of U.S. Pat. No. 5,536,412 (1996) by Abe et al. Here, blood is allowed to flow along one side of a membrane, whereas a suspension of a fine dispersed adsorbing material in a dialysate liquid is pumped, in a pulsation-type flow, along the other side of the membrane. Because of alternating pressure and vacuum, a very intense exchange of liquids through the membrane is accomplished.
All these systems are too complicated to be applied in a short period of time. Besides, they require a very substantial amount of blood to be involved into extracorporeal circuits, which is difficult to be tolerated by the patient.
An original compact plasma filterxe2x80x94sorbent system was suggested by Shettigar et al. (U.S. Pat. No. 5,211,850, 1993). Here, blood is pumped through a hollow fiber membrane-type hemofilter, that is placed into a closed chamber filled with adsorbing material. Plasma is supposed to filtrate into the chamber from the initial portion of the fibers, interact with the sorbent in the chamber and be resorbed through the same membrane in the second part of the fibers. This device minimizes the amount of blood involved into processing and provides an efficient contact between the filtrate, i.e., plasma with the polymer sorbent. A serious disadvantage of such a close device, however, is that it is impossible to observe the movement of the fluids within the device and regulate the flows. Moreover, it is difficult to distribute the adsorbent between the hollow fibers and impossible to separately regenerate and reuse the membrane and the adsorbent material.
Accordingly, it is an object of present invention to provide devices for extracorporeal treatment of physiological liquids of organism, in particular blood, which avoid the disadvantages of the prior art.
In keeping with these objects and with others which will become apparent hereinafter, one feature of the present invention resides in a device which has means forming a filtration membrane for filtering smaller-size components of a physiological fluid withdrawn from a patient from larger-size components of the same; a bed of particulate adsorbing material with which the smaller-size components are contacted for purification; and means for combining the purified smaller-size components of the fluid with the larger-size components of the fluid for returning the thusly treated fluid to a patient.
In accordance with a specific embodiment of the invention, the device has a housing, means forming a blood inlet for introducing blood into the housing and means forming a blood outlet for withdrawing blood from the housing, means forming a hemofiltration membrane which is accommodated in the housing downstream of the blood inlet and formed so that blood cells substantially pass along the hemofiltration membrane directly to the blood outlet while blood plasma is filtered through the hemofiltration membrane from blood cells and flows into an interior of the housing, and a body of particulate adsorbing material accommodated in the housing and located downstream of the hemofiltration membrane so that the blood plasma separated from the blood cells by the hemofiltration membrane passes through the body of adsorbing material which removes toxins from the blood plasma, and the blood plasma after removal of the toxins flows toward the blood outlet to be mixed with the blood cells to be withdrawn through the blood outlet.
When the device is designed in accordance with the present invention, it removes substantially small molecular weight and middle molecular weight toxin molecules from the physiological fluid of organism and no previous separation of blood is needed into the cell-containing component and liquid-containing component. The separation of the cells from the liquid component was (conventionally) performed in the prior art because if the cells also pass through the charcoal or adsorbing resin material, they would be damaged.
The novel features which are considered as characteristic for the present invention are set forth in particular in the appended claims. The invention itself, however, both as to its construction and its method of operation, together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.